Methods for evaluation of easily-reducible iron and manganese in paddy soils

Abstract

ABSTRACT Iron (Fe) and manganese (Mn) toxicity can be an important limitation to flooded rice cropping. Flooding causes several physical and chemical alterations that affect the dynamics of these elements in the soil environment. The objective of this study was to develop procedures of soil analysis, that enable the assessment of easily reducible Fe and Mn availability and uptake by plants. Surface samples (0–20 cm) of ten lowland soils from the State of Minas Gerais, Brazil, were used. The experiment consisted of a factorial randomized block design of ten soils and five liming levels, with five rice plants grown in pots containing 2 dm3 of soil with permanent flooding. The concentrations of Fe and Mn were evaluated in the soil solution and in the aerial parts of the rice plants. The air-dried samples were analyzed for Fe and Mn with sodium-citrate dithionite, ammonium oxalate, Melich-1, 0.1 mol L−1 HCl, ammonium acetate–EDTA, and DTPA–TEA extractants. The Fe concentration in the soil solution was most highly correlated with Melich-1 (r = 0.87), while DTPA–TEA showed the highest correlation with the amount of Fe in the plant (r = 0.62). For Mn, DTPA–TEA was the best predictor of both soil solution Mn and plant Mn (r = 0.87 and r = 0.80, respectively).